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<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <link rel="stylesheet" href="css/public.css">
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<body>
    <div class="square border w-50">1</div>
    <div class="w-50 bg-green">2</div>
    <div class="w-50 border j-center d-flex">
        <div class="w-10 bg-red">a</div>
        <div class="w-10 bg-green">b</div>
        <div class="w-50 bg-yellow">c</div>
    </div>
    <div class="">4</div>
    <div class="border">5</div>
</body>
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</html>